Leviticus 23:39-40

39“You are to celebrate the Lord’s festival on the fifteenth day of the seventh month for seven days after you have gathered the produce of the land. There will be complete rest on the first day and complete rest on the eighth day.

40On the first day you are to take the product of majestic trees — palm fronds, boughs of leafy trees, and willows of the brook  — and rejoice before the Lord your God for seven days.